1. Field of the Disclosure
The present disclosure generally relates to imaging and, more particularly, to an imaging device having a charge roller with improved resistance to defects from prolonged periods of inactivity.
2. Description of the Related Art
Generally, there are two distinct types of charge rollers used in electrophotographic devices such as laser printers. The first type is a charge roller which includes a core material whose surface may be modified by ultraviolet irradiation or chemical treatment. The second type is a charge roller which includes a core material and one or more coating layers. These charge roll types can operate by means of DC type charging or AC plus DC type charging.
It is commonly known that a charge roller may generate defects in a printed image after prolonged static contact with a photoconductor drum, especially if the contact occurs at higher temperature and humidity such as during shipping and warehouse storage. These charge roller defects may be chemical or mechanical in nature and can result in print defects in a printed image of the electrophotographic device.
Chemical defects may be due to the migration or leaching of low molecular weight components of the charge roll core material which may attack the outer surface of the charge roller or the coating layer of the photoconductor drum. This chemical defect may be prevented by the addition of one or more coating layers to the surface of the charge roll core material, which functions as a barrier to prevent chemical migration from occurring.
Mechanical defects may be related to the formation of a dent or flat spot on the outer surface of the charge roller which may be due to the high contact pressure exerted between the charge roller and the photoconductor drum. The resulting print defect of this mechanical defect may be in the form of a repeating horizontal line in the printed image of the electrophotographic device. Furthermore, this mechanical defect may occur even to charge rollers applied with one or more coating layers.
Various separation devices have already been utilized to keep the charge rollers away from contact with the photoconductor drum during shipping or storage. This includes a shipping separator which prevents the charge roller and photoconductor drum from contact during shipping. However, this shipping separator fails to prevent contact of charge roller and photoconductor drum during long periods of electrophotographic device shutdown or power-off. Printers used in schools, for example, may be turned off for the entire summer. A mechanical retract mechanism may be utilized which would disengage the charge roller during power-off. However, this would entail an additional manufacturing and design cost.
A non-contact charge roller may be employed in the electrophotographic device. But this non-contact charge roller may be expensive to create and requires very tight tolerance control of the gap between charge roller and photoconductor drum. Further, this non-contact charge roller requires AC plus DC type charging, thus having a more expensive power supply cost than DC type charge rolls.
Based upon the foregoing, there is a need to provide a charge roller which may withstand relatively high contact pressure with the photoconductor drum even when exposed to relatively high temperature and humidity for an extended period of time. Furthermore, it is desired to have a charge roller that may be resistant to mechanical defects.